Personal information, such as names or social security numbers, are examples of direct personal identifiers. Age, sex, and detailed race and ethnicity are indirect identifiers that might be confidential information. When indirect identifiers are combined with other information, such as geographic identifiers, the combination of information can be used to identify a respondent.
For example, in states with a small population size, knowing the sex, age, race, and cause of death of an individual can lead to identification of the state of residence for an 84-year-old white woman who died from homicide. An Internet search for the terms "white elderly woman killed in STATE X" is likely to reveal the decedent's name.